Staphylococci are common bacterial colonizers of the skin and mucous membranes of humans and other mam mals4. S. epidermidis in particular is the most frequently isolated species from human epithelia. It colonizes predominantly the axillae, head, and nares5. Analysis of the S. epidermidis genome indicated that the species is well equipped with genes assumed to provide protection from the harsh conditions encountered in its natural habitat9, 10. For example, to cope with extremes of salt concentration and osmotic pressure, S. epidermidis has eight sodium ion/proton exchangers and six transport systems for osmoprotectants9.
S. epidermidis belongs to the group of coagulase-negative staphylococci (CoNS), which is distinguished from coagulase-positive staphylococci such as S. aureus by lacking the enzyme coagulase. The species shows a high degree of diversity with 74 identified sequence types (STs)6. Most isolates belong to clonal complex (CC) 2, which comprises the most frequently isolated ST2. Possibly, the successful spread of ST2 may be due to the fact that all ST2 isolates contain IS256 insertion sequences and ica genes7, two factors found correlated with S. epidermidis invasiveness13–16. In addition, most ST2 isolates show in vitro capacity to form biofilms7. Genome information is available for two strains of S. epidermidis: the biofilm-negative ATCC122288 and the biofilm-positive clinical isolate RP62A9. Of note, no genome sequence is available yet for an isolate of the most frequently found and potentially most invasive ST2.